Caldwell was a musical prodigy who before by age 10 six was giving public violin recitals. She graduated from high school at 14 and attended the University of Arkansas and the New England Conservatory of Music. She then served as chief an assistant to Boris Goldovsky at the New England Opera Company for 11 several years, and in the meantime she studied and taught opera at the Berkshire Music Center at Tanglewood, Massachusetts. Her first “solo” production was Ralph Vaughn Vaughan Williams’s Riders to the Sea in 19461947. She headed the Boston University Opera Workshop from 1953 1952 to 19571960, and in 1957 she founded a permanent opera group, which eventually became known as the Opera Company of Boston, for that city; the company closed in the early 1990s owing to financial difficulties.

As conductor and producer there, Caldwell established a reputation for producing daring and inventive variants of standard works; her company gave the original performance versions of Giuseppe Verdi’s Don Carlos and Modest Mussorgsky’s Boris Godunov. She also produced the American premieres of such contemporary operas as Arnold Schoenberg’s Moses und Aron, Luigi Nono’s Intolleranza, and Paul Hindemith’s Mathis der Maler. Her pursuit of meaningful character interpretations and her concern for both musical quality and visual appeal drew to her productions many of the greatest opera singers of the time. In 1976 Caldwell became the first woman conductor of a performance by the Metropolitan Opera in New York City, conducting Verdi’s La Traviata with Beverly Sills in the title role. She also conducted performances by several major symphony orchestras. In 1999 Caldwell joined the faculty at the University of Arkansas, where she headed the school’s opera program and served as distinguished professor of music; she retired in 2004.